Crystal structures and hydrogen bonding in the morpholinium salts of four phenoxyacetic acid analogues

Abstract

The anhydrous salts morpholinium (tetrahydro-2-H-1,4-oxazin-4-ium) phenoxyacetate, C4H10NO+·C8H7O3−, (I), morpholinium (4-fluorophenoxy)acetate, C4H10NO+·C8H6 FO3−, (II), and isomeric morpholinium (3,5-dichlorophenoxy)acetate (3,5-D), (III), and morpholinium (2,4-dichlorophenoxy)acetic acid (2,4-D), C4H10NO+·C8H5Cl2O3−, (IV), have been determined and their hydrogen-bonded structures are described. In the crystals of (I), (III) and (IV), one of the the aminium H atoms is involved in a three-centre asymmetric cation–anion N—H...O,O′R12(4) hydrogen-bonding interaction with the two carboxyl O-atom acceptors of the anion. With the structure of (II), the primary N—H...O interaction is linear. In the structures of (I), (II) and (III), the second N—H...Ocarboxylhydrogen bond generates one-dimensional chain structures extending in all cases along [100]. With (IV), the ion pairs are linked though inversion-related N—H...O hydrogen bonds [graph setR42(8)], giving a cyclic heterotetrameric structure.